I. Field of the Invention
The present invention relates to manufacturing arrays of optical fibers, in particular monomode fibers.
II. Description of the Related Art
The availability of arrays of monomode optical fibers represents a major factor in developing optical technologies and in making them widespread, essentially in the following two fields: firstly optical switching and cross-connection systems using high interconnection density in free space; and secondly motherboard links and integrating components with arrays of fibers. Monomode fiber arrays are key components that are essential for these two fields of activity and that perform the following functions:
inlet and outlet ports for free space optical switches and cross-connection fields; PA1 making arrays of collimated beams in association with arrays of microlenses; PA1 making high density 2D connectors for optical buses; and PA1 coupling arrays of vertical cavity surface emitting lasers (VCSELs) with monomode fiber arrays. PA1 A) N. Basavanhally et al., "Evaluation of fiber arrays for free space interconnect applications", International Topical Meeting on Optical Computing, Salt Lake City, Utah, U.S.A., Mar. 15-17, 1995, Vol. 12, PFB2-1, pp. 124-128; PA1 B) Geoff M. Proudley, C. Stace, H. White, "Fabrication of two-dimensional fiber optic arrays for an optical crossbar switch", Optical Engineering, February 1994, Vol. 33, No. 2, pp. 627-635; PA1 C) J. M. Sassian et al., "Fabrication of fiber bundle arrays for free-space photonic switching systems", Optical Engineering, September 1994, Vol. 33, NO. 9, pp. 2979-2985. PA1 placing optical fibers in an enclosure in the form of a deformable parallelogram, the fibers being in an array of rows and of columns that are at an angle relative to the rows; and PA1 deforming the enclosure so as to vary the angle.
Interconnecting monomode fibers with the required specifications, i.e. positioning accuracy of .mu.m order between fibers, can be achieved for fibers presented in the form of strips. The fibers are placed in respective V-grooves etched in a silicon substrate or machined in a glass or zirconium support. Commercial products are presently available.
Nevertheless, when it comes to interconnecting arrays of fibers, manufacture remains difficult and certain problems have not yet been solved. The solution of stacking strips cannot be used because of the impossibility of controlling the thickness of such strips with .mu.m order accuracy.
Two lines are presently being investigated. The first lies in using a piezoelectric micropositioner to position fibers dynamically in an array of holes that can be made using various methods such as etching a silicon substrate, precision drilling, or ablating metal by means of a laser. Nevertheless, that technique which consists in individually and dynamically aligning and sticking fibers in an array of holes is difficult, lengthy, and very expensive. Furthermore, it does not provide sufficient guarantee that the fibers will be properly positioned angularly in the support so that the axes of the fibers are exactly parallel. The precision with which the fibers are positioned is determined by the regularity of the pitch and the diameter of the holes in the array, and also by the performance of the micropositioner. On this topic, reference can be made in particular to the following documents:
In a second technique, fibers that are bare or that are positioned in microferrules are stacked in a U-shaped support. That technique, which consists in stacking fiber-containing ferrules in a rigid U-shaped frame structure, constitutes a collective assembly method which gives good angular positioning, but which suffers from poor perpendicularity in the array of ferrules, and therefore from excessive positioning errors relative to a reference grid for fibers situated in the corners. Reference can be made in particular to document D) K. Koyabu, F. Ohira, T. Yamamoto, "Fabrication of two-dimensional PANDA fiber array digital free-space photonic switch module", International Topical Meeting on Optical Computing, Sandai, Japan, Apr. 21-25, 1996, Technical Digest Vol. 1, PWC26, pp. 136-137.